A typical dispensing device for supplying a liquid, such as a hot melt adhesive, generally includes a body including a needle having a valve element that blocks and unblocks a fluid outlet. The needle is actuated by an actuator in a first cavity of the body. In pressure-type dispensers, when the fluid outlet is unblocked, the pressured liquid is dispensed as a continuous stream of liquid. In jetting-type dispensers, the striking of the needle against the fluid outlet causes discrete amounts of pressurized liquid to be dispensed.
Dispensing devices further include a fluid channel that directs liquid from a fluid inlet to a fluid outlet. The fluid channel can be located within a second cavity of the body of the dispensing device. The first and second cavities can be connected by a passageway that allows the needle to extend from the first cavity into the second cavity. Because the first and second cavities are open to each other via the passageway, a seal is typically placed within the body of the dispensing device to prevent fluid flow from the second cavity into the first cavity. Inadequate sealing will allow fluid to flow into the first cavity and come into contact with the actuator, which can severely inhibit or disable the actuator.
The operation of dispensing devices with hot melt adhesives can be challenging due to the way certain hot melt adhesives cure. Examples of catalysts to the curing of hot melt adhesives are moisture and heat. Once certain hot melt adhesives are cured, such as polyurethane (PUR) adhesive, they cannot be melted again, as the internal structure of the adhesive has changed. Also, some adhesives can be very difficult to clean using solvents.
During operation of the dispensing device, hot melt adhesive can build up within the fluid flow path and impede the flow of additional liquid. As a result, the dispensing device must be periodically disassembled and a flush material must be passed through the flow path to remove any material remaining within the flow path. The flush material is preferably a compatible material having a similar viscosity as the hot melt adhesive. The amount of material build-up within the flow path is partially determined by the geometric complexity of the flow path, including the presence of any recesses, angled surfaces, threading, etc. Any increase in the amount of material build-up within the flow path increases both the time required to clean the dispensing device and the difficulty of completely flushing liquid from the dispensing device.
Further, a complex flow path can result in flush material remaining within the flow path after cleaning has been completed. Any flush material that remains in the fluid flow path following flushing can compromise the purity of any liquid that subsequently passes through the dispensing device. Decreasing the complexity of the fluid channel and the potential for material build-up within the fluid channel can limit the amount of time a dispensing device is out of operation for cleaning, as well as increase the efficiency and completeness with which flushing takes place, and increase the accuracy with which a user can verify that all flush material has been removed from the fluid channel.
Therefore, there is a need for an improved dispensing device that can be cleaned and/or replaced more easily and effectively.